The invention relates to arrangements for classifying fingerprints for comparison and identification.
A fingerprint is an impression formed by the ridges on the under surface of a finger. The term "fingerprint" herein further includes the ridge pattern of a palm, toe, or sole, and drawings or reconstructions of faint or "latent" fingerprints.
Fingerprints are used in commerce and law enforcement for identification of individuals. Identification is achieved by comparing an unknown fingerprint with a file of reference fingerprints of known identity. For a large reference file, efficient comparison may be facilitated by sorting or classifying the fingerprints according to generalized pattern characteristics or features.
A principal feature is the global pattern formed by the ridges. Common global pattern types have been given descriptive names such as loop, whorl, and arch. Another characteristic is the local pattern formed by the ridges. The points where ridges divide or terminate are called minutiae. A core is a minutia point at the approximate center of a group of recurving or circular ridges. A delta is a minutia point at the approximate center of a group of ridges which form a Y-shape. Other features include, for example, the center of an area enclosed by a recurving ridge.
The atributes of a group of minutia points may be used to generate a classification code. In U.S. Pat. No. 4,135,147 (Riganati et al.), for example, a code for each minutia describes the position and orientation of the minutia relative to neighboring minutiae. In U.S. Pat. No. 3,419,287 (Rudie), the classification code corresponds to the coordinates of minutiae in a coordinate system.
Minutiae, especially the core and delta, also may be useful in classification schemes as reference features or fiducial points. The widely known Henry and FBI National Crime Information Center (NCIC) systems utilize a code in which a first element or descriptor specifies a pattern type, such as loop, whorl, or arch. For loop patterns, a second descriptor is included which is a count of the number of ridges between the core and delta. For whorls, the second descriptor indicates whether the ridge contour from just below the left delta is inside, outside, or meets the right delta. The Henry and NCIC systems, however, provide only a coarse classification in which many thousands of fingerprints may have the same descriptor code. A time-consuming number of comparisons therefore may be required to identify an unknown fingerprint.
It is thus an object of the invention to provide an improved fingerprint classification arrangement in which fewer fingerprints are likely to have the same descriptor codes.